If the uninstaller does not work, your only option is to uninstall manually.
To do this, you will typically have to remove:
- files the software installed
- registry entries it installed
- possibly stop and remove services it installed (not all do this)
Unfortunately, there is no easy way to find out what you need to remove (that's why uninstallers exist). You can try searching for " uninstall manually" to see whether other people had the same problem, maybe you find instructions. Or contact the software's manufacturer (if you have support), failure to uninstall is a major defect in a software.
Otherwise, your only option is to go manually through all folders where the program might be installed, and delete its files. Of course, it goes without saying that you should never do this without a good, recent backup, as you might trash your Windows installation. The same goes for cleaning up the registry.
Ultimately,you may even have to reinstall Windows to get rid of the software if you can't find its files. Alternatively, if this is feasible, you could get/install a clean copy of Windows (possible in a virtual machine), make a list of all files on the HDD, install the SW, then make another list.Compare them to see where the software installed stuff; that's what you have to remove.
But again, there is no safe, foolproof way to deinstall a software that does not have a proper uninstaller, short of reinstalling Windows :-(.